1. Field of the Invention
The present invention relates to rock material characterization, and in particular to characterization of mechanical properties of formation rock from hydrocarbon reservoirs for geological and engineering purposes such as design and planning of well completion, well testing and formation stimulation.
2. Description of the Related Art
Characterization of the mechanical properties of formation rocks in subsurface hydrocarbon reservoirs has become an important feature for exploration and development of oil and gas. The data obtained from characterization has been used in a variety of ways. Characterization data has been used in well planning and completion and for numerous other purposes. Examples include assessing wellbore stability, hydraulic fracture design, mud weight design, geosteering, reservoir characterization, static and dynamic modeling, and reservoir simulation.
The study of geological strata involved on-site collection of geological samples from rock formations of the strata in the well bore while drilling. Characterization data about the mechanical properties of subsurface rock have been obtained by subjecting rock samples (obtained from geological strata at depths of interest in well bores through formations of interest in the reservoir) to special tests in the laboratory.
The collected geological sample material has been in the form of an elongated cylindrical body of rock known as a core sample. The samples once retrieved to the surface through the well were then transported to laboratories for analysis. The laboratories were by definition at some distance from the well and the samples had to be transferred to the lab for testing.
So far as is known, the rock mechanical properties, including strength of the rock sample have been determined from the core sample by testing what were known as core plugs (small cylindrical plugs) taken from the larger original core sample. The smaller plugs from the reservoir core sample are illustrated for example in U.S. Pat. No. 7,126,340, of which applicant is a named inventor. The core plugs taken would then be tested in various types of specialized rock testing equipment according to data requirements and mechanical properties of interest.
After the plugs were extracted, the larger original core sample was then cut or split along its longitudinal axis to expose the interior stratigraphic profile of the core material in a process which is commonly referred to as “slabbing”. The longitudinal section split off from the core sample comprising the core material was often referred to as a “slab”. After slabbing, a rock hardness test could then be conducted using what was known as a scratch test to measure another feature of the formation rock, its hardness. A measure of the hardness of formation rock has served as an indication of the resistance of the formation rock to fracture.
The existing methods to assess rock mechanical properties were thus conducted separately before or after the slabbing procedure. This has been time consuming and costly in terms of time and equipment. Further, existing rock characterization testing frequently did not meet short term or urgent operational needs for data necessary for well completion, well testing and stimulation.